Re: Issue with Synchronization between Manipulate and functions called
- To: mathgroup at smc.vnet.net
- Subject: [mg79001] Re: Issue with Synchronization between Manipulate and functions called
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Sun, 15 Jul 2007 01:10:17 -0400 (EDT)
- Organization: Arcor
- References: <f79rj1$48f$1@smc.vnet.net>
Hi,
Manipulate[Dynamic@ process[a], {a, 1, 10, 1}]
may help ...
Regards
Jens
Nasser Abbasi wrote:
> (Mathematica 6.0, Windows XP, OLD PC)
>
> Manipulate[expr,{n,1,10}] is supposed to evaluate expr for each value
> of 'n'.
>
> There seems to be a synchronization problem between Manipulate[] and
> completing evaluation of expr, when there is a Graphics inside expr.
>
> I have a simple example below, where expr is a function, which
> displays 'n'.
>
> ---- CODE -----------------
>
> process[a_] := Graphics[ {Text[StringJoin["a=", ToString[a]]]},
> ImageSize -> {40} ]
>
> Manipulate[ process[a], {a, 1, 10, 1} ]
>
> ---- END CODE -----------------------
>
> If you run the above, and click on 'play' and look at the display
> inside the Graphics window, you will see that not every integer is
> being printed. i.e. NOT each 'n' is being displayed.
>
> Some values of 'n' are skipped. What is being displayed is something
> like 2,4,6... or 1,2,3,5,6,... instead of 1,2,3,4,5,.... i.e. some numbers
> do NOT get displayed, while Manipulate itself is of course is
> incrementing 'n' correctly. This ofcourse might depend on speed of
> the computer itself and other factors, but on my slow PC, I see this
> is clearly happening.
>
> I think this happens because Manipulate is calling expr before the
> previous Graphics[] which displays the text is fully flushed out to
> display within the function expr.
>
> Hence, expr returns back, and Manipulate now calls it with n+1 value,
> before the previous n value is yet displayed, and so n+1 overwrites
> earlier 'n' in some internal Graphics buffer, and what I see is n+1
> and 'n' is missing.
>
> I need a way to make sure Graphics[] is completed inside expr before
> I return back from the function, back to Manipulate, to prevent this
> problem.
>
> To confirm this, when I 'slow' down Manipulate using the 'slow'
> control, now I see that each number is being displayed ok. So this
> clearly is telling me there is a buffer overrun problem.
>
> I need to study the documentation more, I just started using
> Manipulate, but I noticed this problem.
>
> Do you think I am interpreting this ok, or am I doing something silly
> elsewhere?
>
> thank you
> Nasser
>
>